This invention is concerned with a new and useful process for the production of glucosone and more particularly for the production of glucosone from which food-grade fructose can be obtained.
Commercial methods for the production of fructose, a commercially important sweetner, primarily involve a two-step process, the first, hydrolysis of a polysaccharide such as starch to produce glucose and the second, isomerization of the so-produced glucose to form fructose. The latter step, as is well-known, produces a mixture of glucose and fructose from which it is difficult to separate the desired product, fructose. The commercial separation method involves the use of crystallization and/or fractionation techniques which are costly and time-consuming. More detailed description of the various methods of isomerizing glucose can be found in the literature, e.g. U.S. Pat. Nos. 3,788,945, and 3,616,221.
Glucose can also be converted to fructose by the action of an enzyme, designated glucose-2-oxidase, to form glucosone (D-arabino-2-hexosulose) which in turn can be reduced to fructose with zinc and acetic acid [Folia Micriobiol. 23, 292-298 (1978) and Czechoslovakian Pat. No. 175897 to Volc et al.].
The reaction of glucose-2-oxidase with glucose to produce glucosone also yields hydrogen peroxide in equimolar amount. The use of the so-produced hydrogen peroxide in the conversion of alkenes to corresponding halohydrins and epoxides has been proposed in European Patent Application No. 7176. In the published application, the in situ formation of hydrogen peroxide is proposed by inclusion of glucose-2-oxidase and glucose in the reaction mixture which includes a halogenating enzyme and a source of inorganic halide into which the selected alkene is to be introduced. The disclosure of the European patent application further indicates that the glucosone product of the enzymatic oxidation of glucose can be converted to fructose by simple chemical hydrogenation.
However, fructose produced by the said process can be contaminated with significant amounts of by-products from both the enzymatic conversion of glucose and the alkene conversion reaction. In particular, the latter reaction produces halohydrins and alkylene oxides, e.g. ethylene oxide, which are highly toxic materials even at levels in the region of parts per million. Thus, fructose produced by such a process will require careful and costly purification to attain foodgrade purity. Further, the potential for contamination of fructose by virtue of secondary reactions during the initial processing stage is quite high due to the highly reactive products, halohydrins and alkyleneoxides, and substantial purification procedures are required to assure the high level purity required for food grade fructose.